Work has been underway for the high throughput production of solar cells utilizing “passivated emitter and rear cell” (PERC) and “passivated emitter and rear, totally-diffused” (PERT) device architecture. Both cell designs require that the rear side contains dielectric passivation. The materials of choice, to date, are aluminum oxide (Al2O3) or silicon dioxide (SiO2). The thermal oxidation growth of SiO2 requires temperatures in excess of 900° C. which is the main reason why thermal SiO2 has not been implemented; silicon bulk lifetime is highly sensitive to high-temperature processes. Al2O3 can be deposited by various techniques such as atomic layer deposition (ALD), plasma enhanced chemical vapor deposition (PECVD), and reactive sputtering. Some of the drawbacks of these are that they increase the process steps and that the equipment required can be costly to own and operate.
In most PERC and PERT architectures, the rear side must be devoid of a diffused layer. Industrially, this is achieved by etching back the parasitic emitter utilizing a solution containing various concentrations of HF, HNO3, and H2SO4. This etching process leaves behind a damaged surface that lowers the effective lifetime of silicon and so is then removed utilizing KOH.